WASHINGTON, USA (AFP) — US President Barack Obama's campaign launched a fierce attack yesterday on Mitt Romney, accusing the White House hopeful of lying about how long he remained head of his firm Bain Capital.

The Obama campaign seized on a Boston Globe report citing government records that appear to show the Republican remained in control of the private equity firm for three years beyond the 1999 date he said he had stepped down.

Obama's team unleashed a withering assault on Romney in the aftermath of the report, warning the challenger may have committed a felony

if he misrepresented his position at Bain to federal regulators.

The date could be important, as Bain Capital is alleged to have invested in firms that moved workers overseas after 1999 and Obama supporters are attempting to paint Romney as a destroyer of jobs.

The Globe said that, despite Romney's announced departure, public Securities and Exchange Commission (SEC) documents filed by Bain state he remained its "sole stockholder, chairman of the board, chief executive officer and president".

The report said financial disclosure forms from 2003 showed Romney owned 100 per cent of Bain Capital in 2002, and earned a corporate salary of at least $100,000 in 2001 and 2002.

The Romney campaign dismissed the report as inaccurate, and Bain Capital issued a statement saying Romney left the firm in February 1999 to run the Olympics.

Romney has had "absolutely no involvement with the management or investment activities of the firm or with any of its portfolio companies since the day of his departure," the company said.

But it added that "due to the sudden nature of Mr Romney's departure, he remained the sole stockholder for a time while formal ownership was being documented and transferred to the group of partners who took over management of the firm in 1999," and was reported in various capacities on SEC filings during the period.

The protracted row over Romney's time at Bain and whether he or Obama is more responsible for sending US jobs offshore has emerged as a central issue in the run-up to the election. Both sides are using highly personal attacks as they craft narratives of their rivals that undermine voters' trust ahead of November.

Bain is the primary source of Romney's vast wealth, estimated at about $250 million, and the ex-businessman's finances are at the core of some of the uncertainty surrounding Romney, the former governor of Massachusetts.

Romney has insisted he was not responsible for Bain-owned companies that went bankrupt or laid-off workers after he stepped back from the firm's day-to-day business in order to manage the Winter Olympics in Salt Lake City.

"Now, we know that he wasn't telling the truth," charged Obama Deputy Campaign Manager Stephanie Cutter in a statement.

Cutter said the report links him to "troubling investments involving outsourcing and bankruptcies" and raises questions about whether

he misrepresented his departure date.

Critics have hit out at Romney for the Swiss bank account he once held and for investments he has in Bermuda and The Cayman Islands, alleging he used offshore financial centres to avoid US taxes.

Romney has released only his 2010 tax returns and an estimate for 2011, and Obama and his Democrats have heaped pressure on him to release more tax data from previous years.

"He could not even become cabinet member for that lack of disclosure, and now with that lack of disclosure he wants to be president of the United States," House Democratic leader Nancy Pelosi said.

Cutter launched a broadside in a conference call, saying Romney may have been "misrepresenting his position at Bain to the SEC, which is a felony."

Or, "he was lying to the American people" by misrepresenting his position at Bain.

"That's a real character and trust issue that the American people need to take very seriously," she added.

Romney's Campaign Manager Matt Rhoades lashed out at Cutter's "reckless and unsubstantiated comments," and called on Obama to "apologise for the out-of-control behaviour of his staff."

In its own recent ad, the Romney campaign said Obama "doesn't tell the truth" about Romney's business record, and blamed the president for shipping jobs overseas even as he pledged to bring jobs back to US shores.

And Republican Speaker of the House John Boehner challenged Obama on his own outsourcing record.

Americans "have a right to know where the hell the Obama administration shipped their tax dollars overseas during a recession here at home," said Boehner.

"I think the president owes every American

an explanation."